The present invention relates to a non-aqueous electrolyte battery. More specifically, the present invention relates to a non-aqueous electrolyte containing an additive for suppressing an increase in the internal resistance of the battery.
In recent years, there has been a rapid advancement in the realization of small and lightweight electronic devices, and along with that, there has also been an increased demand for batteries having high energy densities. Accordingly, intensive researches have been made on lithium primary batteries having a negative electrode comprising metallic lithium as well as lithium ion secondary batteries having a negative electrode comprising a carbon material.
In such batteries, as a solvent for constituting the non-aqueous electrolyte, propylene carbonate, ethylene carbonate, butylene carbonate, sulfolane, xcex3-butyrolactone, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, dioxolane and the like are used singly or as a mixture. Further, as a solute to be dissolved in the solvent, LiClO4, LiPF6, LiBF4, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2 are used singly or as a mixture.
Recently, intensive researches have been made on lithium polymer batteries containing a gel non-aqueous electrolyte or a solid polymer electrolyte. The gel nonaqueous electrolyte contains a host polymer for retaining the solute and the solvent as described above. The solid polymer electrolyte is an electrolyte in which the polymer itself functions as the solvent for the solute, and a polymer similar to the host polymer contained in the gel non-aqueous electrolyte is used, for example.
As the polymers constituting these electrolytes, derivatives formed on the basis of polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polysiloxane and the like are used.
These constituting elements of the non-aqueous electrolytes are known to chemically react with moisture and the electrodes, and also with a material constituting a separator inside the battery. In particular, metallic lithium, lithium alloys such as LiAl, LiSn and the like and carbon materials capable of absorbing and desorbing lithium, which constitute the negative electrode, are highly reactive with the constituting elements of the non-aqueous electrolytes, and they form an organic coating film on the surface of the negative electrode by chemical reactions and the like. In particular, such phenomena are likely to occur when the batteries are stored in a high temperature atmosphere of 80xc2x0 C. or higher, or when the charge/discharge cycle is repeated of the secondary batteries. Metal oxides often used as a positive electrode active material of the non-aqueous electrolyte batteries are known to dissolve in the non-aqueous electrolyte, and a phenomenon can be observed that materials dissolved are deposited on the surface of the negative electrode to form a coating film.
Since these films have low electrical conductivity, they constitute a cause for increasing the internal resistance of the batteries. When batteries are stored for a long time, the voltage drop at discharging due to the increase of the internal resistance of the batteries is increased, making it impossible to obtain satisfactory discharge characteristics. In secondary batteries, there is the problem that the internal resistance of the batteries is increased by repetition of the charge/discharge cycle, thereby deteriorating the cycle characteristics.
A-suggestion has been made intending to suppress the increase in the internal resistance of the batteries by adding, to the non-aqueous electrolyte, additives for forming a coating film on the surface of the negative electrode. As such additives, aromatic dicarboxylic acid esters are mentioned in Japanese Laid-Open Patent Publication No. Hei 7-22069. These additives are effective for batteries stored at room temperature; however, they have no effects on batteries stored at high temperatures or in which the charge/discharge cycle is repeated.
The present invention intends to prevent formation of an organic coating film on the surface of the negative electrode caused by chemical reactions when storing the nonaqueous electrolyte batteries at high temperatures, to suppress an increase in the internal resistance in primary batteries and secondary batteries, and to improve the charge/discharge cycle characteristics of secondary batteries.
The present invention relates to a non-aqueous electrolyte battery having a negative electrode comprising metallic lithium, a lithium alloy or a material capable of absorbing and desorbing lithium; a positive electrode; a solvent; and a solute dissolved in the solvent, wherein the above non-aqueous electrolyte contains at least one additive selected from the group consisting of compounds represented by the general formula (1): 
where X1 to X4 are independently hydrogen atoms, F, Cl, Br, I or alkyl groups having 1 to 3 carbon atoms, Y1 is a hydrogen atom, Na, K, Rb, Cs, Mg, Ca, Sr or Ba, and i is 1 or 2; compounds represented by the general formula (2): 
where X5 to X8 are independently hydrogen atoms, F, Cl, Br, I or alkyl groups having 1 to 3 carbon atoms, Y2 is a hydrogen atom, Na, K, Rb, Cs, Mg, Ca, Sr or Ba, and j is 1 or 2; and compounds represented by the general formula (3): 
where Y3 is a hydrogen atom, Na, K, Rb, Cs, Mg, Ca, Sr or Ba, and k is 1 or 2.
In the above non-aqueous electrolyte, the content of the above additive is preferably 0.001 to 10% by weight relative to the sum of the solvent and the solute.
The solute is preferably at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiCF3SO3, LiAsF6, lithium salts represented by the general formula (4):
LiN(CmX92m+1Z1)2,
lithium salts represented by the general formula (5):
LiC(CnX102n+1Z2)3,
and lithium salts represented by the general formula (6):
LiCR(CpX112p+1Z3)2
where X9 to X11 are independently F, Cl, Br or I; m, n and p are independently integers of 1 to 4; and Z1 to Z3 are independently CO or SO2.
The aforementioned solvent preferably comprises at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate and xcex3-butyrolactone.